Advanced Custom Fields plugin : displaying a field while omitting the p tags

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strip_tags() is not bad, but there may be a lot of tags you’ll have to allow. So maybe you can use str_replace() to only get rid of the <p>-tag:

<?php 
  $field = get_field('wysiwyg'); // your wysiwyg field data
  $strip = array('<p>','</p>'); // search for <p>
  echo str_replace($strip,'',$field);
?>